Albert J. Thiel, © 1997
In Part 1 we touched on the reproduction of Cyanobacteria (the table listed various methods of reproduction): binary fission, budding, fragmentation. These forms of reproduction explain to a great extent the various appearances that Cyanobacteria take on in the aquarium: patches, slimy masses, strings, filaments, branched filaments and so on. We have seen that photosynthesis plays a large and important role in the reproduction and growth of such algae. The wavelength of the lighting that you provide determines what form of Cyanobacteria will grow in the tank. Keep the wavelengths that particularly promote blue-green algae growth low and you will have far less problems. We have also noted that other nutrients play a role in growth and reproduction (dissolved organic carbon or material being an important one). Phosphate and iron are other ones. Because of the usually high amount of pigments present in Cyanobacteria (as mentioned in Part 1), and because these pigments assist in the photosynthesis process (both PS I and PS II or Photsystem I and II), light does plays a great role in their growth and bears looking at some more. Indeed, slime algae of various colors can appear when the light source has degraded and when the wavelengths mentioned in Part 1 are suddenly becoming stronger (more intense or appear as a greater proportion of the total amount of lighting provided that penetrates the water. This is often overlooked. Hobbyists are more likely to look for other reasons to explain the blue-green growths, and forget that old bulbs, fluorescents tubes, and other forms of lighting may need to be replaced to eliminate the spectra that are undesirable in terms of their effect on Cyanobacterial growth in general. Photosynthesis can best and in its easiest form be described as the synthesis of organic compounds through the uptake of carbon dioxide and its fixation, light being used as the energy source. The total process involves several complex enzymatic and energy requiring reactions, all of which follow each other in a very particular order. I will not go into the details and mention the various enzymes involved such as carbonic anhydrase, dark reactions and other terminology that is not necessary to understand what is actually going on. For more information on those processes you can refer to specialized books or articles in the Review of Microbiology. What is important to note is two-fold at least:
The carbon dioxide can come from the breakdown of organic material but can also come from bicarbonate ions. Note, therefore, that a high dissolved organic load, combined with a high dKH, is practically certain to lead to the appearance of blue-greens. Note also that higher or greater amounts of photosynthesis, with at the same time the presence of a great deal of organic material in the water, will produce more CO2 on one hand and increase growth on the other. Higher amounts of light combined with more CO2 provide more energy and since the carbon dioxide is present, blue-greens will start to grow. The ideal combination for blue-greens to grow is: high DOC (dissolved organic carbon = dissolved organic protein = dissolved organic matter and the decay of that organic matter), high dKH levels and over saturation of CO2. The latter can occur if and when the carbon dioxide is not degassed properly from the water through the overflow leading to the sump, or when the water enters the sump by falling down in it in small streams. If no sump is present at all the likelihood of carbon dioxide being high increases. Add to that lighting ot the type of wavelengths indicated in Part 1 and you are just about sure to get blue-green algae to grow in your aquarium. Add a high dKH and you really have an ideal environment for Blue-Greens to appear and proliferate and be hard to eradicate. As you can see it does not take much really for Cyanobacteria to grow in our tanks! I should perhaps add an explanation on why bicarbonates can contribute to the amount of blue-greens. Bicarbonates (such as baking soda - another reason not to use it often or on a large scale to maintain pH levels which it does not really do anyway since its natural pH is between 7.6 and 7.8) is converted to carbon dioxide by means of an enzymatic process: HCO3- +H+ turns into CO2 + H2O. CO2 does not require light necessarily. That is why such carbon dioxide fixation is referred to as the "dark reaction" of photosynthesis. Carbon dioxide can be uptaken even when no light is present. When other conditons are not favorable to the growth of Blue-Greens, they will not appear in your tank. If they are though, they will. Other conditions, and in my experience, the one that contributes most to the growth of blue-greens is the presence of high amounts of dissolved organic material which really creates an ample supply of carbon dioxide and the presence of phosphates. Since photosynthesis is at work, photolysis occurs (also called the Hill Reaction) and oxygen is produced as a by-product. This is normally only associated with macro green algae but it should be clear from what has been written here that this oxygen production and release occurs with blue green algae as well. The actual reaction breaks water up into 2 Hydrogen ions, half an oxyen one and 2 units of energy. This explains why blue-greens soon are covered with tiny bubbles. The bubbles are free oxygen. While this free oxygen greatly contributes to dissolved oxygen levels in the tank, the fact that it is generated by algae we do not really want in our aquarium, makes it a process we do not wish to rely on. In nature though, blue-green algae are a very important source of oxygenation and play a very positive role in maintaining water quality at high purity since free oxygen has a real high ORP and cleans the water a great deal. In aquariums though we wish to achieve oxygen saturation in other ways, not through blue-green algae. It was stated that the kind of lighting that is provided affects the growth cycle and determines the type of Cyanobacteria that actually make their appearance is a major factor to consider. What differentiates Cyanobacteria from other algae that photosynthesize, and especially from Chlorophyta (the higher green algae) is the wavelengths at which photosynthesis can take place. I indicated that chlorophyll plays a role and that the ideal wavelength for this process is the 665-680 nanometers wavelength. Specific to Cyanobacteria and what makes them different and may lead to their appearance is when the light emitted by whatever bulb you use, start to shift and emits wavelengths in the 620 and 560 nanometer range where the phycobiliproteins referred to in Part 1 are just as efficient at photosynthesing than chlorophyll is. This is a major difference specific to Blue-Greens, and is pointed out by several Authors consulted while writing this article. At those wavelengths phycocyanin and phycoerythrin photosynthesize and lead to the appearance of Cyanobacteria. A slight shift in the amount of light emitted in this waveband can therefore lead to an outbreak of Blue-Greens. Unsuspecting Hobbyists may try to find all kinds of reasons for this growth when all that is really happening is that their bulbs need changing as they are emitting light that is promoting the growth of Blue-Greens. Mind you, chlorophyll is still involved in the process but what is happening is that the pigments that can uptake the shorter wavelengths transfer it to the ones that need higher ones and so on. A typical sequence of the full photosynthesis cycle of Cyanobacteria would then be: » energy uptake and transfer from phycoerythrin to phycocyanin, to allophycocyanin, to chlorophyll a. The rest is quite clear. As photosynthesis proceeds and all the processes start to take place, Blue-Green algae suddenly appear in the aquarium. Note that the picture is more complex still in certain cases and that other pigments and other nutrients are involved as well in the growth. Perhaps this explains why when these algae appear it is so difficult to deal with them and also explains why they appear when we as Hobbyists believe our water quality parameters are such that none should grow. Remember though: the main culprits are dissolved organic material and carbon dioxide and light of the wavelengths indicated above. More will be reviewed in Part 3 of this article which I hope to have ready within a week or so. As you can well imagine this article requires a great deal of reading and then distilling the information in article form. At the end of the series I will list references and suggested reading materials that you may wish to consult if you want to research this further. Should you have any questions feel free to Email Me |